ARM64: Optimize generated code for gaps

src/arm64/assembler-arm64.h

Index: src/arm64/assembler-arm64.h
diff --git a/src/arm64/assembler-arm64.h b/src/arm64/assembler-arm64.h
index 8774c09603bb035220f8fd843c69580a94e1100d..6e1bb74e79be75525e7f522e0d7bf2146a72055a 100644
--- a/src/arm64/assembler-arm64.h
+++ b/src/arm64/assembler-arm64.h
@@ -707,6 +707,16 @@ class MemOperand {
   // handle indexed modes.
   inline Operand OffsetAsOperand() const;
 
+  enum PairResult {
+    kNotPair,   // Can't use a pair instruction.
+    kPairAB,    // Can use a pair instruction (operandA has lower address).
+    kPairBA     // Can use a pair instruction (operandB has lower address).
+  };
+  // Check if two MemOperand are consistent for stp/ldp use.
+  static PairResult AreConsistentForPair(const MemOperand& operandA,
+                                         const MemOperand& operandB,
+                                         int access_size_log2 = kXRegSizeLog2);
+
  private:
   Register base_;
   Register regoffset_;